feat: add ZDR support to Rust implementation (#642)

This adds support for the `--disable-response-storage` flag across our
multiple Rust CLIs to support customers who have opted into Zero-Data
Retention (ZDR). The analogous changes to the TypeScript CLI were:

* https://github.com/openai/codex/pull/481
* https://github.com/openai/codex/pull/543

For a client using ZDR, `previous_response_id` will never be available,
so the `input` field of an API request must include the full transcript
of the conversation thus far. As such, this PR changes the type of
`Prompt.input` from `Vec<ResponseInputItem>` to `Vec<ResponseItem>`.

Practically speaking, `ResponseItem` was effectively a "superset" of
`ResponseInputItem` already. The main difference for us is that
`ResponseItem` includes the `FunctionCall` variant that we have to
include as part of the conversation history in the ZDR case.

Another key change in this PR is modifying `try_run_turn()` so that it
returns the `Vec<ResponseItem>` for the turn in addition to the
`Vec<ResponseInputItem>` produced by `try_run_turn()`. This is because
the caller of `run_turn()` needs to record the `Vec<ResponseItem>` when
ZDR is enabled.

To that end, this PR introduces `ZdrTranscript` (and adds
`zdr_transcript: Option<ZdrTranscript>` to `struct State` in `codex.rs`)
to take responsibility for maintaining the conversation transcript in
the ZDR case.

codex-rs/core/src/codex_wrapper.rs

@@ -21,6 +21,7 @@ use tracing::debug;
 pub async fn init_codex(
     approval_policy: AskForApproval,
     sandbox_policy: SandboxPolicy,
+    disable_response_storage: bool,
     model_override: Option<String>,
 ) -> anyhow::Result<(CodexWrapper, Event, Arc<Notify>)> {
     let ctrl_c = notify_on_sigint();
@@ -33,6 +34,7 @@ pub async fn init_codex(
             instructions: config.instructions,
             approval_policy,
             sandbox_policy,
+            disable_response_storage,
         })
         .await?;